Sore shoulder and arm after surgery

Your body has been through a trauma and knows it, you may have had nerves damaged that are healing and you're stitching yourself up on the inside anyway so you can expect some odd things. I had a lot of pain in my arm after surgery too, not because of the surgery itself but because while I was unconscious during the surgery I was posed for hours with my arm above my head so they could access the breast. I woke up with stabbing sensations and joint pain in addition to all the other bunk.
...and then I went and slept on my arm funny too :lol:. 
Have a talk to your doctor about it, especially if there's any tingling or stiffness.